Rundown Velocity Along the Slope of a Breakwater with
Keywords:Rundown velocity, breakwater, accropode, rubble mound, runup, float, wave steepness
Rundown velocity along the slope of a breakwater is quite an important parameter in breakwater design. Literature review on rundown velocity measurements indicates that a few small scale studies have been attempted in the past, mostly along beach slopes. This paper details the experimental investigations conducted at large wave flume (GWK), Franzius Institute, Hannover, Germany, in regard to rundown velocity along the slope of a rubble mound breakwater with an accropode armour layer. As the wave flume facilitates generation of wave heights in the range of 0.20 to 2.0 m with wave period ranging between 3.0 and 12.0 seconds, measurements on rundown velocity for the near prototype conditions were possible. Two methods were adopted to determine rundown velocity viz., (i) with a float and (ii) with a wave gauge. The results on the variation of rundown velocity with Iribarren Number and wave steepness are presented in the form of non-dimensional graphs and discussed.
The studies indicated that for identical wave input parameters float method predicts a higher value of rundown velocity compared to wave gauge method. For instance, with a wave height of 0.6 m and wave period of 5.8 seconds, float method predicts a rundown velocity of 1.7 m/sec as against 1.24 m/sec predicted by wave gauge. The experimental results strongly predict the dependency of rundown velocity on wave period, in addition to wave steepness and Iribarren Number The trend curves of rundown velocity show the existence of an upper boundary below which all trend curves lie regardless of the wave period. Present experimental investigations provided valuable information about the magnitude of rundown velocity along breakwater slope which hitherto was not available to the engineers dealing with breakwaters.